1. Field of the Invention
The present invention relates generally to the field of air or gas bearing structures and more particularly to an air or gas bearing structure compatible with a high vacuum environment.
2. Brief Description of the Prior Art
In the electron semiconductor industry, electron beam devices are used in the manufacture of the semiconductor wafers and masks. Generally speaking, these electron beam devices require a high vacuum environment to perform their function efficiently. Most of these devices mount their target wafers or masks on a moveable platform known as a stage. These stages are normally required to move in an X-Y plane in many minute and precise movements.
There are many problems providing an air bearing in a high vacuum environment. The problems have heretofore been approached by providing the air bearing external to the vacuum chamber with the stage mounted on an arm extending into the vacuum chamber. This solution has the inherent problems of instability at the end of the arm.
Another solution is to provide high vacuum pumps at the periphery of the air bearing to remove the air as it exits the periphery of the air bearing. However this solution is both nonideal and very expensive.
A third solution is provided in U.S. Pat. No. 4,191,385 to Fox, deceased, et al. In this solution the vacuum chamber is provided interior of the air bearing. This solution has the inherent problems of a large massive structure. Minute, precise movements are not indicated.